Ultrasound transducer assembly

ABSTRACT

An ultrasound catheter is disclosed for providing substantially real-time images of small cavities. The ultrasound catheter is characterized by separate and distinct materials for backing the transducers and for carrying the electronics components. The separate materials comprise an electronics carrier meeting the requirements for holding the integrated circuitry of the ultrasound device and a backing material displaying superior characteristics relating to reducing ringing and minimizing the effect of other sources of signal degradation in the transducer assembly. Also, in accordance with the present invention, a technique is described for connecting the conductor lines of the separate transducer assembly and electronics body.

INCORPORATION BY REFERENCE

The applicants hereby incorporate by reference the description of an“Apparatus and Method for Imaging Small Cavities” described in Proudianet al. U.S. Pat. No. 4,917,097, the description of a “Dilating andImaging Apparatus” described in Eberle et al. U.S. Pat. No. 5,167,233,and the description of an “Apparatus And Method For Detecting Blood FlowIn Intravascular Ultrasonic Imaging” in O'Donnell et al. U.S.application Ser. No. 08/234,848, filed Apr. 28, 1994 (issue fee paid,and patent number not yet assigned).

FIELD OF THE INVENTION

The present invention relates generally to the field of ultrasonicimaging, and more particularly to ultrasonic imaging to determinevarious characteristics of relatively small cavities and surroundingfluids and structures.

BACKGROUND OF THE INVENTION

Diagnosis and treatment of fully or partially blocked arteries of theheart is essential in the medical profession's endeavor to prevent heartattacks.

Physicians have successfully prevented heart attacks arising from arteryblockage caused by the build-up of plaque upon the walls of the coronaryarteries through the use of percutaneous transluminal coronaryangioplasty (PTCA, commonly referred to as “balloon angioplasty”).Balloon angioplasty involves carefully threading a catheter into theaffected portion of the artery. After the balloon portion is determinedto be properly positioned in the artery, the physician inflates theexpandable portion of the catheter in order to broaden the blocked ornarrowed passage in the blood vessel caused by the deposition of plaqueupon the artery wall.

The desirability of using an imaging device to produce treatment anddiagnostic quality images of small enclosed areas such as human bloodvessels on a diagnostic video display device is unquestioned. It isknown to use a very small ultrasonic imaging device mounted at the endof a catheter to produce a real-time image of the internal walls of acoronary artery. This device is referred to herein as an ultrasoundcatheter.

In the known ultrasound catheters, the same material is used for theelectronics carrier upon which a set of electronic components aremounted and for the backing material for the transducer assembly. Adrawback to the known ultrasound catheters is the difficulty in findinga carrier/backing material which provides the physical and acousticqualities desired for advantageous use as the carrier for theelectronics and the backing material for a transducer assemblycomprising a highly sensitive transducer material.

The known ultrasonic catheter structure, though providing the advantageof design and construction simplicity, exhibits certain drawbacksattributable to the particular and mutually incompatible requirementsfor the backing material and the electronics carrier. It is desirablethat the electronics carrier for the electronics body be rigid andcapable of withstanding the elevated temperatures produced by theelectronics. However, the known electronics carrier materials whichsatisfy the requirements for the electronics body are not suitablebacking materials for the presently preferred transducer assembliescomprising highly sensitive lead zirconate titanate (PZT) composites.

When the new, more sensitive PZT composites are used with the knownelectronic carrier material as the backing material for the transducer,unwanted ringing occurs in the transducer assembly when an acousticsignal is received or transmitted by the catheter. The signal producedby the ringing reduces the quality of the signal transmitted by thetransducer assembly and limits the foreseeable advantages of utilizingthe more sensitive transducer materials in ultrasonic catheters. Thedecreased signal quality attributed to the ringing limits the-imagequality provided by an ultrasound catheter. The limited image qualityrestricts the usefulness of the ultrasound catheter for clinical anddiagnostic imaging.

In known ultrasound catheters the transducer electrodes are coupled tothe transducer layer through a capacitive glue layer. As was previouslymentioned, PZT composites having a relatively high degree of sensitivityto acoustic signals are being considered for replacement of thepreviously used, less sensitive, ferroelectric polymer transducermaterials. While the PZT composites exhibit superior sensitivity incomparison to the ferroelectric copolymers, they also have a higherdielectric constant. The reduced impedance (or increased capacitance)associated with the new PZT composites significantly negates theimproved signal sensitivity provided by the PZT composites when coupledto the transducer electrodes through the capacitive glue layer.

SUMMARY OF THE INVENTION

It is an object of -the present invention to provide a superiorvirtually real-time ultrasonic image of relatively small cavities andtheir surrounding tissues than previously obtainable in the prior art.

It is a further object to provide enhanced sensitivity to reflectedsignals from the walls of a cavity in order to provide improved imageresolution.

It is a further object of the invention to meet the other objectives andmaintain or reduce ringing and other sources of noise in a signaltransmitted or received by the transducer assembly and to therebyprovide a clearer image of a cavity.

It is yet another object of the present invention to provide a means formore easily fabricating the very small transducer elements of thetransducer assembly of an ultrasound catheter.

It is yet another object of the present invention to provide a means forforming the very small transducer elements for the ultrasound catheterto very close tolerances.

It is another object of the present invention to provide desirablecarrier/backing materials for the electronics body and transducerassembly of an ultrasound catheter.

It is yet another object of the present invention to provide a means forjoining the conductor lines of the electronics body to the conductingelectrodes of the transducer assembly in order to provide a signal pathbetween the separately fabricated sections containing the integratedcircuits and the transducer assembly of an ultrasound catheter.

The above objects are met by a catheter probe assembly of the presentinvention comprising a multi-sectioned body for insertion into a cavity.The multi-sectioned body is characterized by separate and distinctcarrier/backing materials for an electronics body and a transducerassembly. The present invention comprises a probe assembly for anultrasound catheter generally of the type described in Proudian deceasedet al. U.S. Pat. No. 4,917,097 and Eberle et al. U.S. Pat. No. 5,167,233for producing substantially real-time images of small cavities and theirsurrounding tissue.

The transducer assembly, comprising an array of transducers is mountedupon a first section of the multi-sectioned body. The transducer arraytransmits ultrasonic acoustic waves to the cavity and generateselectrical signals in response to reflected ultrasonic acoustic wavesreceived by the transducers.

The backing material for the transducer assembly is specificallyselected for its characteristic low acoustic impedance and highabsorption. The low acoustic impedance backing material absorbs signalscoupled into the backing material and reduces the presence of ringing inthe transducer assembly. In addition, a set of transducer electrodes aredirectly bonded to the transducer material thereby eliminating acapacitive glue layer previously associated with the transducercircuits.

Integrated circuits are mounted upon a second section of themulti-sectioned body. The second section, acoustically isolated from thefirst section, comprises a carrier material having a low thermalexpansion coefficient. The integrated circuits receive a set of firstelectrical signals from the transducer array by means of electricalconductors interconnecting the transducer assembly electrodes and thepads of the integrated circuits. The electrical conductors are also usedto transmit excitation signals from the integrated circuits to thetransducer assembly. The integrated circuits convert the received firstelectrical signals into a second set of electrical signals. Then theintegrated circuits transmit the second set of signals to a signalprocessor located outside the environment of the cavity by means of acable.

The unique, multi-sectioned, structure of the probe assembly enables thedesigner of the probe assembly to separately select a materialexhibiting the preferred structural and acoustic characteristic for thecarrier of the integrated circuit components and the backing materialfor the transducer elements.

In order to prevent damage to the components of both the transducerassembly and the electronics body, these two portions of the ultrasoundcatheter probe assembly are separately manufactured and linked duringthe final stages of fabrication of the ultrasonic catheter.

BRIEF DESCRIPTION OF THE DRAWINGS

The appended claims set forth the features of the present invention withparticularity. The invention, together with its objects and advantages,may be best understood from the following detailed description taken inconjunction with the accompanying drawings of which:

FIG. 1 is a side cross-sectional view of the tip of a catheterillustrating the electronics body, the transducer assembly, and theballoon section of a balloon angioplasty ultrasound imaging catheterembodying the present invention;

FIG. 2 is a perspective view of the tip of a partially constructeddiagnostic imaging catheter prior to joining the signal paths betweenthe separated electronics body and transducer assembly;

FIG. 3 is a detailed side cross-sectional view of the tip of the imagingdevice portion of the catheter showing the composition of the imagingdevice;

FIG. 4 is a cross-sectional view of the transducer assembly taken alongline 4-4 in FIG. 1;

FIGS. 5 a and 5 b illustratively depict an alternative embodiment of theultrasound catheter wherein the conducting electrodes in the transducerassembly extend beyond the backing material and the transducer material;

FIG. 6 is a side cross-sectional view of the tip of a catheterillustrating the electronics body, transducer assembly, and noseassembly of an ultrasound diagnostic imaging catheter embodying thepresent invention;

FIGS. 7 a and 7 b show cross-sectional and side-sectional views of analternative embodiment of the present invention wherein the transducerarray is configured to provide a “side-looking” view; and

FIGS. 8 a, 8 b and 8 c show side, forward, and top cross-sectional viewsof an alternative embodiment of the present invention wherein thetransducer array is configured to provide a “forward-looking” view.

While the invention will be described in connection with a catheter usedfor angioplasty, it will be understood that it is not intended to belimited to such use. On the contrary, the invention is intended to coverall applications which may require imaging in a small cavity. An exampleof such an alternative would be the use of the present invention on acatheter without the balloon. In such a case, the catheter acts as adiagnostic or monitoring device. Another specific alternative use of thepresent invention is for measuring blood flow rates using Doppler soundimaging in conjunction with the present invention. The present inventionmay also be used to produce internal images of a number of ducts withina body such as the monitoring of gall stones in the bile ducts and forexamination and treatment in the area of urology and gynecology. Anotherexample of an application of the present invention is the use of theultrasound catheter for providing an image of a vessel or duct duringapplication of laser treatment or during the removal of plaque from thewalls of a vessel during an antherectomy procedure.

Furthermore, this invention may be applied to other types of transducerarray configurations which will be known to those of ordinary skill inthe art in view of the description of the invention and the accompanyingdescriptions of various embodiments of this invention contained herein.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Though the present invention concerns the structure of thecarrier/backing material for the electronics body and transducerassembly and changes to the physical layers of the transducer assembly,the invention is intended to be incorporated in general into anultrasound catheter imaging system of the type described in Proudian,deceased et al. U.S. Pat. No. 4,917,097 the teachings of which areincorporated herein by reference. Furthermore, the present ultrasoundcatheter may be used to obtain images using a number of differentimaging techniques including, for example, the imaging techniquedescribed in O'Donnell et al. U.S. application Ser. No. 08/234,848,filed Apr. 28, 1994 (issue fee paid), the teachings of which areexpressly incorporated herein by reference.

A cross-sectional view of a catheter embodying the present invention isillustratively depicted in FIG. 1. The catheter shown in FIG. 1 carryinga balloon 1 is of is the type which is generally used for angioplasty;however, the invention can be used in conjunction with a number ofcatheter designs such as those illustratively depicted in FIGS. 6, 7 and8 to provide diagnostic images and deliver treatment to small cavitiesof the body. Conventional guide wire lumens 2 and 3 are telescopicallyfitted over a mating radiopaque guide wire lumen 4 forming a centralbore 6 for a catheter guide wire during a normal catheterizationprocedure. An encapsulant 8 composed of an epoxy material secures animaging device 10 comprising the electronics body 12 and the transducerassembly 14 to the end of a catheter shaft 16. The imaging device 10 inaccordance with the present invention contains a multi-sectioned bodycomprising separate and distinct materials for a carrier 20 and atransducer backing material 24. The encapsulant 8 protects and insulatesa set of integrated circuits (IC's) 18 mounted upon the carrier 20. Inthe preferred embodiment of a balloon angioplasty device embodying thepresent invention, the imaging device 10 is positioned within a proximalsleeve 19 of the balloon 1.

The transducer assembly 14, described hereinafter in greater detail inconjunction with FIG. 3, generally comprises a set of transducerelements 22. The transducer elements 22 are supported in a cylindricalshape about the backing material 24. However, other transducer elementconfigurations will be known to those skilled in the area of transducerdevices in view of the present description and in view of the state ofthe art.

Continuing with the description of FIG. 1, the balloon 1 is positionedadjacent the imaging device 10 and is isolated from ambient conditionsby sealing the two ends of the balloon 1 to the catheter shaft 16 andthe lumen 3 in a conventional manner. A tube 26 is embedded within theencapsulant 8 for communicating a fluid between the balloon 1 and aninflation source. Within the expandable portion of the balloon 1 andattached to the lumen 3 is a radiopaque marker band 27 to assist inlocating the position of the catheter on a fluoroscope.

A cable 28 comprising an inner and outer set of wires carries electronicdata and control signals between the IC's 18 and a control stationcomputer. Each inner wire in the cable 28 is formed from a solidconductor protected by an insulating coating. The outer wires arespiraled a number of times around the cable 28 in order to shield thesignals carried by the inner wires of the cable 28. Preferably, thecable is coated with an insulating material.

Turning now to FIG. 2, a perspective view is provided of the tip of apartially constructed diagnostic imaging catheter 10 prior to joiningthe signal paths between the separated electronics body 12 andtransducer assembly 14 in order to show the distinct first and secondportions of the imaging device 10 comprising the transducer assembly 14and the electronics body 12. To aid the description of the imagingdevice 10, the proximal sleeve 19 and the epoxy encapsulant 8 coveringthe imaging device 10 have been removed to expose the integrated circuitchips 18 and associated electronic constructions. A nose cone 25provides a blunted lead surface for the ultrasound imaging catheter inorder to prevent damage to a vessel as the catheter is guided throughthe vessel.

The radiopaque guide wire lumen 4, visible within a patient by means ofa fluoroscope, aids in the positioning of the catheter. The radiopaqueguide wire lumen 4 also holds both the electronics body 12 and thetransducer assembly 14. The outer diameter of the radiopaque guide wirelumen 4 is approximately 0.5 millimeters. The radiopaque guide wirelumen 4 provides the additional function of acting as a guide forprecisely positioning the electronics body 12 and transducer assembly 14in order to mate a set of 64 conductor lines 30 from the IC's 18 mountedupon the electronics body 12 to a set of 64 transducer contacts 32 ofthe transducer assembly 14 in a manner shown in FIG. 3. In order for theradiopaque guide wire lumen 4 to assist in mating the above describedcomponents of the imaging device 10, the gap between the radiopaqueguide wire lumen 4 and both the carrier 20 and the backing material 24must be very small and should not be greater than approximately 25 μm.This minimized gap ensures proper radial alignment of the conductorlines 30 and transducer contacts 32.

In order to physically place the IC's 18 onto the carrier 20, the fourIC's 18 are of an inverted chip design known to those skilled in thearea of the semiconductor chip fabrication art and are bonded to a setof conductive pads 34 formed on the carrier 20. The conductive pads 34interconnect the IC's 18 to their neighboring chips and provide aconnection between the IC's 18 and the cable 28 that communicativelycouples the IC's 18 to a signal processor located outside the patient.The pads also connect the IC's 18 to the conductor lines 30. Theconductor lines 30 link the IC's 18 to a set of 64 electrodes thatdefine the transducer elements in the transducer assembly 14.

Each of the IC's 18 has 16 channels associated with 16 transducerelements defined by 16 transducer electrodes in the transducer assembly14. Each of the four IC's 18 is responsible for sequentiallytransmitting and receiving electrical signals in the ultrasonicfrequency range on one or more of its 16 channels linked by conductorlines 30 to an associated transducer element in the transducer assembly14. The four IC's 18 provide a multiplexing function that distributesexcitation pulses from a signal processor to one or more of thetransducer elements. At any given time one or more of the 16 channels oneach of the IC's 18 is free to be excited by an excitation signal or toreceive reflections or echoes by means of activation control signalsstored on the IC's 18. The electrical signals generated from thereflections impinging on the active transducer elements are amplifiedand sent via the transmission cable line 28 to the external signalprocessor.

Turning to FIG. 3 a detailed side cross-sectional view of the imagingportion of the catheter of FIG. 1 is illustrated to show the structureand materials of the imaging device 10. In this drawing the electronicsbody 12 and the transducer assembly 14 are shown in their mated state asthey would exist in the final construction of the imaging catheter.Though the layers of the transducer assembly are shown in detail in FIG.3 it will be helpful to refer to FIG. 4, a cross section view of thetransducer assembly taken along line 4-4 of FIG. 2, during thedescription of the ringed layers of the transducer assembly 14.

The carrier 20 is bonded to the radiopaque guide wire lumen 4 by meansof a glue layer 36 comprising any commercially available medical gradecyanoacrylate epoxy. One may substitute any material or structure thatsatisfactorily immobilizes the electronics body 12 for the glue layer36. As previously mentioned the space between the radiopaque guide wirelumen 4 and the carrier 20 filled by the glue layer 36 must be verysmall in order for the radiopaque guide wire lumen 4 to assist in thematching of the electrical contacts between the electronics body 12 andthe transducer assembly 14.

The carrier 20 in the preferred embodiment of the invention is formedfrom a rigid, strong material having a low thermal expansioncoefficient. The carrier 20 must be capable of withstanding temperaturesin excess of 200 degrees Celsius to which the electronics body 12 issubjected during the process of bonding the set of IC's 18 to thecarrier 20. Furthermore, during operation of the ultrasound catheter,self-heating of the IC's 18 may cause expansion of the carrier 20 if thethermal expansion of the carrier 20 is too great, shear forces exertedby the carrier 20 upon the conductive pads 34 create a substantial riskof failure of the electrical connection between the contacts of the IC's18 and the conductor lines 30. Aluminum oxide (Al₂O₃) possesses theaforementioned desired characteristics for the carrier 20; however,other suitable substitutes for this material are well known to thoseskilled in the art of hybrid circuits. Aluminum oxide is alsocharacterized by a very high acoustic impedance (approximately 40MRayls) and relatively low loss. As will be explained below, theseacoustical properties make Aluminum oxide a poor candidate for use asthe transducer backing material for applications involving highlysensitive transducer elements.

An encapsulant 8 is, applied to the outer surface of the electronicsbody 12 in order to provide a more cylindrical shape to the catheterassembly and to insulate the electronic circuitry. The encapsulant 8generally comprises any commercially available medical grade UV-curableacrylic. In order to guard against contamination of the blood andpossibly electrical shock, the outside of the electronics body may becovered by a protective layer. The protective layer is made of, forexample, parylene. Other suitable materials for the protective layerwill be known to those skilled in the art of ultrasound catheters orother medical instruments which are inserted within the body. Theprotective layer consists of the proximal sleeve 19 in the balloonangioplasty catheter shown in FIG. 1 or a sheath 38 in the case of adiagnostic imaging catheter such as the one illustrated in FIG. 6.

Turning to the transducer assembly 14 and its related structures, thebacking material 24 for the transducer assembly 14 is preferably formedfrom a material characterized by a relatively low acoustic impedance(<10 MRayls) and high loss coefficient (on the order of 20 to 40 dB/mm).This is necessitated by the use of highly sensitive transducer materialssuch as the PZT composites used for a transducer material 40 whosesuperior signal sensitivity is otherwise negated by the ringing effectcaused by a backing material having a high acoustic impedance and lowloss. For this reason, Aluminum oxide is not a preferred material forthe backing material 24 for the transducer assembly 14. Instead, aseparate and different material is used to form the backing material 24for the ultrasound catheter of the present invention. A preferredmaterial for the backing material 24 is an epoxy resin filled witheither rubber particles or glass microspheres. An example of such aresin is “light-weld” 183-M by Dymax Corp., Torrington, Conn. Othersuitable materials having low acoustic impedance and high loss will beknown to those of ordinary skill in the art of ultrasound imaging.Although air is an ideal backing material, transducer assemblies usingan air backing are difficult to achieve in practice.

Thus, the ultrasound catheter of the present invention is characterizedby an imaging device 10 having separate and distinct carrier/backingmaterials that exhibit greatly contrasting characteristics. The twodistinct materials provide desirable structural and acousticalcharacteristics for satisfying the dissimilar requirements for theelectronics body 12 and the transducer assembly 14.

In the preferred method of making the transducer assembly 14, the outerlayers of the transducer assembly 14 are separately manufactured as aplanar sheet. They comprise a first set of 64 conducting electrodes 42,the transducer material 40, a continuous layer conducting electrode 44,and a matching layer 46. After the layers are fabricated, the planarsheet of transducer elements 22 is wrapped around the backing material24 and bonded by means of a glue layer 48. Depending on the mechanicaland acoustic properties of the transducer assembly 14, physicalisolation of the transducer elements 22 from one another may bedesirable. Since a uniform distribution of each of the transducerelements 22 is desired, the outer diameter of the backing material 24must be manufactured within very close tolerances so that the ends ofthe planar sheet of transducer elements, when joined to form a cylinderaround the backing material 24, meet with minimal gap or overlap.Alternatively, the planar transducer assembly 14 may be formed into acylinder of exact outer diameter concentrically around the radiopaquelumen 4 and the gap between the lumen 4 and the transducer assembly 14is filled with the backing material 24. This ensures that the spacingbetween the transducer array elements at the opposite ends of thecylindrically wrapped planar sheet have the same spacing as the othertransducer array elements. It is believed that the error in thecircumference of the transducer sheet, when wrapped around the lumen 4,should be less than (plus or minus) 8 μm. Furthermore, the innerdiameter of the backing material 24 must closely match the outerdiameter of the radiopaque guide wire lumen 4 in order to facilitate themating of electrical contacts between the electronics body 12 and thetransducer assembly 14. The concentric rings comprising theafore-described layers of the transducer assembly 14 are illustrativelydepicted in FIG. 4 showing a cross-sectional view of the transducerassembly taken on line 4-4 of FIG. 1.

An advantage of the planar sheet transducer element fabrication methodis the absence of capacitive glue layers previously present between thetransducer material 40 and each of the conducting electrodes 42 and 44.If the capacitive glue layer remained in the presently describedultrasound catheter, an increased capacitance attributable to the higherdielectric constant of the PZT composite transducer material 40 wouldnegate the improved signal sensitivity of the preferred transducermaterial. There are several other advantages to the sheet approach tofabricating the transducer array. Fabrication on a flat surface iseasier than on a curved, cylindrical surface. This is especiallyimportant in transducer assemblies wherein the transducer material 40must be separated (or diced) in order to form the transducer material onthe continuous conducting electrode 44 as individual elements instead ofa continuous sheet. The capability of fabricating the transducermaterial 40 as individual elements is an important factor when choosinga particular fabrication method in view of the desirability of lowcross-talk (less than −30 dB), which may necessitate such a separationof elements. Some of the possible manufacturers of the planar sheetscomprising the transducer elements are: Precision Acoustic Devices,Fremont, Calif.; Acoustic Imaging, Phoenix, Ariz.; Echo Ultrasound,Lewistown, Pa.; Vermon S. A., Tours, France; and Imasonic, Besancon,France.

After the transducer assembly 14 has been formed, it may be desirablefor the transducer material to be polarized by means of a high voltageon the order of 5,000 Volts applied between the first set of conductingelectrodes 42 and the continuous conducting electrode 44. Therefore, itis desirable to perform the polarization procedure on a separatedassembly to isolate the transducer assembly 14 from the electronics body12 since application of such a high voltage to the IC's 18 would destroythe electronic circuitry of the IC's 18.

The layer of glue 48 bonds the backing material 24 to the first set ofconducting electrodes 42 spaced evenly about the circumference of thebacking material 24. The first set of conducting electrodes 42 definesthe individual transducer elements in the transducer array. The firstset of conducting electrodes 42 is attached to the set of 64 transducercontacts 32. Connection material 50 electrically couples each one of thetransducer contacts 32, corresponding to a single transducer element, toa corresponding one of the conductor lines 30, thereby providing anelectronic signal path between the transducer elements 22 and the IC's18. The connection material comprises any of several known suitableconductors such as silver or gold loaded epoxy droplets, solder or goldbumps, or solder tape.

There are other connection schemes for joining the conducting electrodes42 to the conductor lines 30. FIGS. 5A and 5B illustratively depict analternative embodiment of the ultrasound catheter wherein copperconducting electrodes 42 of the transducer assembly 14 extend beyond thebacking material 24 and the transducer material 40. The portion of theconducting electrodes 42 extending beyond the backing material 24 andoverlapping the conductor lines 30 when the transducer assembly 14 isjoined to the electronics body 12 facilitates the use of a well knowngap welder to fuse the individual conductor lines 30 to thecorresponding conducting electrodes 42.

FIG. 5A shows a cross-sectional view of a partially constructedultrasound catheter to show the above described connection scheme. Theuse of a gap welder eliminates the need to deposit individual drops ofsolder material 50 as shown in FIG. 3. The elimination of solderdroplets potentially simplifies the design of the electronics carrier 20that may otherwise require scalloping of the carrier at the endproximate the transducer assembly 14 in order to facilitate properdeposition of the droplets to fuse the conductor lines 30 and thetransducer contacts 32. Other advantages of this connection schemeinclude better bonding of the conductors, simpler assembly techniques,and enhanced mechanical stability.

Another advantage of the connection scheme portrayed in FIGS. 5A and 5Bis the potential to automate the process of bonding the conductingelectrodes 42 to the conductor lines 30. As shown in the cross-sectionalview of a partially assembled ultrasound catheter assembly in FIG. 5B,the conductor lines 30 are matched to the conducting electrodes 42.Next, a tip 70 of a gap welder is placed above one of the matched lines.The tip 70 presses a conducting electrode 42 a to a correspondingconductor line 30 a. A low voltage, high electrical current passesbetween the electrodes of the tip 70. The electrical current fuses theconducting electrode 42 a to the conductor line 30 a. Next, the catheterassembly is rotated so that a next matched set of lines (42 b and 30 b)is below the tip 70 and the welding process is repeated. The weldingcontinues until all the lines have been fused.

Returning now to ultrasound imaging device in FIG. 3, there exists arange of suitable transducer materials which can be used to transduceelectrical energy into acoustic energy and vice versa in the Megahertzfrequency range. In the preferred embodiment of the present invention,the efficiency rating of the transducer material, expressed in terms ofthe coupling coefficient k_(t), is high (greater than 50%); thebandwidth should be high (greater than 50% of center frequency); thereshould be good matching among the transducer elements; there should below insertion loss (less than −40 dB); and the center frequency shouldbe around 20 MHz. Therefore, in the preferred embodiment of the presentinvention, the transducer material 24 is any one of many known suitablePZT composites. A summary of the properties of the PZT composites isprovided in Acoustic Waves: Devices, Imaging, and Analog SignalProcessing, by Professor Gordon S. Kino, Prentice-Hall, Inc., 1987 atpages 554 and 555. Generally, these composites may be damaged bytemperatures exceeding 75° Celsius and could not be present when thebonding of the IC's 18 to the carrier 20 occurs.

The radial thickness of the transducer layer 40 is preferably one-halfwavelength thickness or an odd multiple of half wavelengths of theintended center operating frequency of the ultrasound catheter. Asexplained in Biomedical Ultrasonics, at page 53, this enables thetransducer to resonate at the center operating frequency of theultrasound catheter. In the present embodiment, the radial thickness ofthe transducer material 24 is approximately 0.1 millimeters.

In order to take advantage of the superior signal sensitivity oftransducers formed from PZT composites, the backing material 24 musthave a low acoustic impedance. Therefore, the aluminum oxide carrier 20having a high acoustic impedance should not be used as the backingmaterial 24. Instead the previous monolithic carrier for both theelectronics body 12 and the transducer assembly 14 is replaced by theseparated carrier/backing sections 20 and 24.

The continuous conducting electrode 44 covering the outer surface of thetransducer material 40 is the ground plane for the transducer elements22. It is preferably a layer of gold metal deposited upon the surface ofthe matching layer 46 by means of sputtering. However, other suitableconductors and methods to deposit the conductor will be known to thoseskilled in the art of transducers fabrication. Though not essential tothe proper operation of the ultrasound catheter, it is preferred toconnect in a known manner the continuous conducting electrode 44 to aground line provided by the cable 28. The ground line runs along theelectronics carrier 20 and is connected to the continuous conductingelectrode after the electronics body 12 and the transducer assembly 14have been joined. One possible way to connect the ground wire is shownin FIG. 2 of the Proudian, deceased et al. U.S. Pat. No. 4,917,097.

The transducer elements 22 are enclosed by a matching layer 46. Asexplained in Biomedical Ultrasonics, by P. N. T. Wells, Academic Press1977, at page 54, the efficiency of transmission into the load may beincreased by an impedance matching layer of quarter wavelengththickness. In the presently preferred embodiment the matching layer 46comprises a loaded epoxy and is approximately 0.06 mm. thick.Alternative appropriate matching layer materials and their thicknesseswill be apparent to those of ordinary skill in the art of ultrasonicimaging.

After independent construction, the electronics body 12 and thetransducer assembly 14 are bonded together by a layer of glue 52 and theelectrical connections between the electronics body 12 and thetransducer assembly 14 are electrically coupled in a manner previouslydescribed. The cable 28 containing the leads from the signal processorfor the ultrasound catheter (previously described in the Proudian et al.'097 patent) are bonded to the conductive pads 34 on the carrier 20 in aknown manner.

FIG. 6 shows an alternative embodiment of the present invention, whereinthe imaging device 10 is included in a diagnostic imaging catheter thatdoes not contain a balloon 1. Portions of the diagnostic imagingcatheter have been removed to reveal the cable 28 and the lumen 2. Sincethere is no balloon 1 in the imaging catheter shown in FIG. 6, there isof course no tube 26 for filling and draining a fluid from the balloon.Instead, the catheter is fitted with a nose cone 25. The nose cone 25provides a blunted lead surface for the ultrasound imaging catheter inorder to prevent damage to the walls of a cavity as the catheter isinserted. A sheath 38 covers the epoxy resin 8 thereby guarding againstcontamination of a patient's blood and possibly electrical shock. Thesheath 38 is preferably constructed of parylene, though other suitablesubstitutes will be known to those skilled in the art of medicalinstruments that are inserted within a body. The structure of theimaging catheter shown in FIG. 6 is otherwise unchanged from thestructure of the balloon angioplasty ultrasound imaging catheterillustrated in FIG. 1.

Though the preferred embodiment of the present invention contains atransducer array configured as a cylinder about a cylindrical core,there are numerous other configurations of ultrasound catheters thatembody the present invention. Examples of such configurations are shownin FIGS. 7 and 8. Other configurations of transducer arrays for anultrasound catheter will be known to those skilled in the art in view ofthe present description of this invention.

FIGS. 7A and 7B illustrate side and cross-sectional views of aside-looking linear array imaging catheter.

In this arrangement the transducer elements 22 are arranged in a planeand perpendicular to the direction of insertion of the imaging catheter.This arrangement provides an image along the length of a cavity. In thisalternative embodiment of the present invention, the IC's 18 areconnected to the cable 28 in the same manner as the previously describedembodiments of the invention. Furthermore, in accordance with thepresent invention, the IC's 18 are mounted upon an electronics carrier20 of the type previously described in connection with the preferredembodiment of the invention shown in FIG. 1. The IC's are electricallycoupled to the transducer elements 22 by conductor lines 30. The backingmaterial for the transducer elements 22 forms the encapsulant 8 in thiscase.

FIGS. 8A, 8B and 8C illustrate side, forward, and top cross-sectionalviews of a forward-looking “endfire” imaging catheter shown in FIG. 1.In FIGS. 8A, 8B and 8C the encapsulant 8, which is also the backingmaterial for the transducers 22, has been partially removed to revealthe placement and orientation of the electronics portion. In thisarrangement the transducer elements 22 are arranged as a planar arraymounted upon the leading face of the catheter. The guide wire lumen 4 ismounted adjacent the ultrasonic imaging device. The diameter of theguide wire lumen 4 is approximately 0.3 mm or about one-third thediameter of the imaging catheter.

This arrangement provides a forward looking view of a cavity. Thedimensions of the field of view are determined by the size of the array,the number of elements, the element dimensions and frequency. In thisalternative embodiment of the present invention, the IC's 18 areconnected to the cable 28 in the same manner as the previously describedembodiments of the invention. Furthermore, in accordance with thepresent invention, the IC's 18 are mounted upon a carrier 20 of the typepreviously described in connection with the preferred embodiment of theinvention shown in FIG. 1. The IC's are electrically coupled to thetransducer elements 22 by conductor lines 30. The encapsulant 8 may formthe backing material for the transducer elements 22.

It will be appreciated by those skilled in the art that modifications tothe foregoing preferred embodiment may be made in various aspects. Thepresent invention is set forth with particularity in the appendedclaims. It is deemed that the spirit and scope of that inventionencompasses such modifications and alterations to the preferredembodiment as would be apparent to one of ordinary skill in the art andfamiliar with the teaching of the present application.

1. An ultrasound catheter probe for insertion into a vasculature andemitting ultrasonic acoustic waves and providing transduced electricalsignals arising from ultrasonic echoes of the ultrasonic acoustic waves,said ultrasound catheter probe comprising: a multi-sectioned body havingdistinct sections for independently supporting a transducer array andintegrated electronic circuitry, the multi-sectioned body comprising: afirst section, comprising a first material, serving as a transducerbacking and having a relatively high acoustic energy absorption incomparison to a second section, comprising a second material, forsupporting integrated electronic circuitry; a transducer assembly,supported by the first section of the multi-sectioned body, includingthe transducer array for transmitting the ultrasonic acoustic waves intothe vasculature and generating electrical signals in accordance with theultrasonic echoes of the ultrasonic acoustic waves; and integratedelectronic circuitry, supported by the second section of themulti-sectioned body, for receiving the electrical signals generated bythe transducer assembly and, in response to the electrical signals,transmitting information to an environment external of the vasculature.2-19. (canceled)